Download - Transmission Line
TO DESIGN PLAN ERECTION OF A HIGH
TENSION LONG TRANSMISSION LINE
ELECTRICAL DEPARTMENT
IDEAL INSTITUTE OF ENGINEERING
Presented By:Pritam Debnath
Introduction
The term high voltage characterizes
electrical circuits in which the voltage used
is the cause of particular safety concerns &
insulation requirements. High voltage is
used in electrical power distribution, in
cathode ray tubes, to generate x-rays &
particle beams, to demonstrate arcing, for
ignition, in photomultiplier tubes & high
power amplifier vacuum tubes & other
industrial & scientific applications .
Types of Transmission Line
There are two types of Long Transmission line.
1)Extra High Voltage (EHV)
2)Ultra High Voltage (UHV)
We will discuss about the EHV type only.
WHAT IS EHV TRANSMISSION ?
Two factors considered in the classification of
a "high voltage" are the possibility of causing
a spark in air, and the danger of electric shock
by contact or proximity.
In electric power transmission engineering,
high voltage is usually considered any
voltage over approximately 35,000 volts.
In electric power transmission engineering
this refers to equipment designed for more than
345,000 volts between conductors. In
electronics systems, a power supply that
provides greater than 275,000 volts is known
as an "EHV Power Supply". It is often used in
experiments in physics.
With the increase in transmission voltage, for same amount of
power to be transmitted current in the line decreases which reduces
I2R losses. This will lead to increase in transmission efficiency.
With decrease in transmission current, size of conductor required
reduces which decreases the volume of conductor.
The transmission capacity is proportional to square of operating
voltages. Thus the transmission capacity of line increases with
increase in voltage.
With increase in level of transmission voltage, the installation cost of
the transmission line per km decreases.
It is economical with EHV transmission to interconnect the power
systems on a large scale.
The no. of circuits and the land requirement for transmission
decreases with the use of higher transmission voltages.
The major advantages are:
Reduction in the current.
Reduction in the losses.
Reduction in volume of conductor material required.
Decrease in voltage drop & improvement of voltage regulation.
Increase in Transmission Efficiency.
Increased power handling capacity.
The no. of circuits & the land requirement reduces as transmission
voltage increases.
The total line cost per MW per km decreases considerably with the
increase in line voltage.
The major disadvantages are:
Corona loss & radio interference
Line supports
Erection difficulties
Insulation needs
The cost of transformers, switchgear equipments & protective
equipments increases with increase in transmission line voltage.
The EHV lines generates electrostatic effects which are harmful to
human beings & animals.
DISTRIBUTION LINE WITH NO GROUND WIRE
Dual 345 KV transmission lines
In addition to phase conductors, a transmission line usually includes one or two
steel wires called ground (shield) wires. These wires are electrically connected to
the tower and to the ground, and, therefore, are at ground potential.
In large transmission lines, these
wires are located above the
phase conductors, shielding them
from lightning.
A typical line route will involve the use of three main types of tower. They are as follows:
1) Suspension Tower
2) Deviation Tower
3) Terminal Tower
TYPES OF POLES
Type & Size of Conductors
An overhead transmission line usually consists of three conductors or
bundles of conductors containing the three phases of the power system.
The conductors are usually aluminum cable steel reinforced (ACSR),
which are steel core (for strength) and aluminum wires (having low
resistance) wrapped around the core.
Transmission lines are characterized by a series
resistance, inductance, and shunt capacitance
per unit length. These values determine the power-
carrying capacity of the transmission line and the
voltage drop across it at full load.
ERECTION OF HT LINE
Erection of HT line includes installation of poles/towers, stringing of conductors, Earthing of poles, fixing of anticlimbing device, etc.
Installation of poles/towers.
Stringing of conductors.
Earthing of poles.
Anticlimbing Device.
Danger Signboard.
Corona
Sag
Skin Effect
Ferranti Effect
SAG CALCULATION
Sag determines electrical clearances, right-of-way width(blowout),uplift (strain),thermal rating
Sag is a factor in electrical & magnetic fields, Aeolian vibration (h/w),ice galloping
Tension determines structure angle/dead end/broken wire loads
Tension limits determine conductor system safety factors, vibration & structure cost
Sag D
Span
Tension H
D (sag at belly)
Max tension
(s/2,d)end support
H=horizontal component of Tension(lb)T=Maximum tension(lb)x, y=Wire location in x y coordinates(0,0) is the lowest point(ft)D=Maximum sag(ft)L=Conductor length(ft)w=Conductor weight(lb/ft)S=Span length(ft)
SAFETY ASPECTS:
Clearance.
Earthwire.
Voltages of greater than 50 V applied across dry unbroken
human skin are capable of producing heart fibrillation if they
produce electric currents in body tissues which happen to pass
through the chest area.
The electrocution danger is mostly determined by the low
electrical conductivity of dry human skin.
(International safety symbol "Caution, risk of electric shock" (ISO 3864), colloquially
known as high voltage symbol)
Accidental contact with high voltage supplying sufficient energy will
usually result in severe injury or death.
low-energy exposure to high voltage may be harmless, such as the
spark produced in a dry climate when touching a doorknob after walking
across a carpeted floor.
1) Other factors (e.g. neighbourhood factors, square footage, size of lot, irrigation potential) are much more likely than overhead transmission lines to be major determinants of the sales price of property.
2) Effects are most likely to occur to property crossed by or immediately next to the line, but some impacts have been measured at longer distances.
3) Positive impacts may also occur, where the right-of-way is attractively landscaped or developed for recreational use.
4) Impacts may be greater for smaller properties than for larger properties.
REFERENCES
1) Project in Electrical, Electronics, Instrumentation and Computer Engineering by Dr. S.K.Bhattacharya & Dr.S.Chatterjee.
2) Principles of Power System by V.K.Mehta & Rohit Mehta
3) www.nationalgrid.com/uk/senseofplace
4) http://www.electrical4u.com/ferranti-effect-in-power-system/
5) http://www.electrical4u.com/skin-effect-in-transmission-lines/
6) Power System Engineering, Nagrath & Kothery, TMH.
7) Elements of power system analysis, C.L. Wodhwa, New Age International.
8) Electrical Power System, Ashfaq Hussain, CBS Publishers & Distributors.
9) A Text book on Power system Engineering, Soni, Gupta, Bhatnagar & Chakrabarti, Dhanpat Rai & Co.
10) http://www.google.com/
THANK YOU